Previous work by the principal investigator has established that the presence of free sulfhydryl (-SH) groups in hemoglobin is neither a necessary nor a sufficient condition for normal cooperative interactions or a nearly normal Bohr effect in the oxygenation equilibrium, although the oxygen affinity may be increased by -SH group blockage. The oxidation-reduction potential is affected in a similar way. Present work is being directed toward elucidation of possible mechanisms by which different -SH reagents affect these parameters in different ways. Replacement of reactive -SH groups by other groups, such as -OH, is also under investigation. The effects of environmental conditions (pH, temperature, urea organic phosphates and other salts), enzymatic treatment (e.g., carboxypeptidases), and treatment with -SH reagents, cyanate, and other reagents of different sizes, polarities, configurations and group-specificities are being and will be investigated with respect to oxygen equilibrium, oxidation-reduction equilibrium, Bohr effects, molecular conformation (tertiary structure), chain-chain interactions (quaternary structure), reaction kinetics, and other physicochemical properties of various hemoglobins. These will continue to include human hemoglobins A (Adult Hb), A sub 3, F (Fetal Hb), S (Sickle-cell hemoglobin) and bovine hemoglobin, as well as the hemoglobin chains of which these hemoglobins are composed.